In a mobile communication system, a user equipment (UE) may receive information from a base station in downlink, and the UE may transmit information in uplink. The information which may be transmitted or received by the UE includes data and a variety of control information. There are various physical channels depending on the kind and use of information transmitted or received by the UE.
FIG. 1 is a view showing physical channels used for a 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) system, which is an example of a mobile communication system, and a general signal transmission method using the same.
When a UE is powered on or when the UE newly enters a cell, the UE performs an initial cell search operation such as synchronization with a base station in step S101. To this end, the UE may receive a Primary Synchronization Channel (P-SCH) and a Secondary Synchronization Channel (S-SCH) from the base station so as to perform synchronization with the base station, and acquire information such as a cell ID. Thereafter, the UE may receive a physical broadcast channel from the base station and acquire broadcast information in the cell. Meanwhile, the UE may receive a Downlink Reference signal (DL RS) in the initial cell search step and confirm a downlink channel state.
The UE which completes the initial cell search may receive a Physical Downlink Control Channel (PDCCH) and a Physical Downlink Shared Channel (PDSCH) corresponding to the PDCCH, and acquire more detailed system information in step S102.
Meanwhile, the UE which does not complete the access to the base station may perform a random access procedure in steps S103 to S106, in order to complete the access to the base station. To this end, the UE may transmit a specific sequence via a Physical Random Access Channel (PRACH) as a preamble (S103), and may receive a message in response to the random access via the PDCCH and the PDSCH corresponding thereto (S104). In contention-based random access except for handover, a contention resolution procedure including the transmission of an additional PRACH (S105) and the reception of the PDCCH and the PDSCH corresponding thereto (S106) may be performed.
The UE which performs the above-described procedure may then receive the PDCCH/PDSCH (S107) and transmit a Physical Uplink Shared Channel (PUSCH)/Physical Uplink Control Channel (PUCCH) (S108), as a general uplink/downlink signal transmission procedure.
FIG. 2 is a view explaining a signal processing procedure in which a UE transmits an uplink signal.
In order to transmit the uplink signal, a scrambling module 201 of the UE may scramble a transmitted signal using a UE-specific scrambling signal. The scrambled signal is input to a modulation mapper 202 so as to be modulated into complex symbols using Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK) or 16-Quadrature amplitude modulation (QAM)/64-QAM scheme according to the kind of the transmitted signal and/or the channel state. Thereafter, the modulated complex symbols are processed by a transform precoder 203, and the processed complex symbols are input to a resource element mapper 204. The resource element mapper 204 may map the complex symbols to time-frequency resource elements used for actual transmission. The signal processed as described above may be transmitted to a base station via an SC-FDMA signal generator 205 and an antenna.
FIG. 3 is a view explaining a signal processing procedure in which a base station transmits a downlink signal.
In the 3GPP LTE system, the base station may transmit one or more codewords in downlink. Accordingly, one or more codewords may be processed to configure complex symbols by scrambling modules 301 and modulation mappers 302, similar to the uplink transmission of FIG. 2. Thereafter, the complex symbols are mapped to a plurality of layers by a layer mapper 303, and each layer may be multiplied by a predetermined precoding matrix, which is selected according to the channel state, by a precoding module 304 and may be allocated to each transmission antenna. The processed signals which will respectively be transmitted via antennas may be mapped to time-frequency resource elements used for transmission by resource element mappers 305, and may respectively be transmitted via OFDM signal generators 306 and the antennas.
In a mobile communication system, in a case where a UE transmits a signal in uplink, a Peak-to-Average Ratio may be more problematic than the case where a base station transmits a signal in downlink. Accordingly, as described above with reference to FIGS. 2 and 3, the downlink signal transmission uses an OFDMA scheme, but the uplink signal transmission uses an SC-FDMA scheme.
Hereinafter, a procedure for multiplexing data or control information before a signal is transmitted in uplink or downlink will be described with reference to FIGS. 4 and 5.
FIG. 4 is a view showing a procedure for multiplexing data and control information which will be transmitted in uplink.
As shown in FIG. 4, with respect to data multiplexed with control information, a Transport Block (TB) Cyclic Redundancy Check (CRC) is attached to a TB to be transmitted in uplink (S401), the TB is segmented into several Code Blocks (CBs) according to the size of the TB (S402), and a CB CRC is attached to the several CBs (S403). Channel coding is performed with respect to the result value (S404). In addition, channel-coded data is subjected to rate matching (S405), CBs are concatenated (S406), and the concatenated CBs are then multiplexed with the control signal (S407).
Meanwhile, with respect to a Channel Quality Information (CQI)/Precoding Matrix Index (PMI), a CRC is attached (S408), and channel coding is then performed independent of the data (S409). The channel-coded CQI/PMI is subjected to rate matching (S410) and is then multiplexed with data (S407).
In addition, with respect to rank information, channel coding is performed independent of the data (S411). The channel-coded rank information is subjected to rate matching (S412) and is then multiplexed with data (S407).
The multiplexed data, CQI/PMI and rank information is subjected to channel interleaving (S413).
In case of ACK/NACK information, channel coding is performed independent of the CQI/PMI and rank information (S414), the ACK/NACK information is inserted into some of the interleaved signals through a puncturing process, and the interleaved signals, into which the ACK/NACK information is inserted, are mapped to physical resources (S415) and are then transmitted in uplink.
FIG. 5 is a view showing a procedure for multiplexing data which will be transmitted in downlink.
As shown in FIG. 5, with respect to the data, a TB CRC is attached to a TB to be transmitted in downlink as an example of an error detection unit (S501). Thereafter, a TB having a length of at least a specific bit number may be segmented into a plurality of CBs, and a CB CRC may be attached to the CBs as another example of the error detection unit (S502).
In the 3GPP LTE system, the specific bit number may be 6144 bits corresponding to the size of the interleaver during channel coding, and one TB which does not exceed 6144 bits is mapped to one CB without modification. At this time, one TB which is not segmented into CBs may correspond to one codeword. At this time, the procedure may progress to step S503 in a state in which the step of attaching an additional CB CRC to one TB (CB) of FIG. 2 is omitted.
Meanwhile, if the length of one TB exceeds the specific bit number, one TB may be segmented into a plurality of CBs. At this time, each of the segmented CBs may correspond to one codeword. With respect to the plurality of codewords, the above-described channel coding for error correction is performed (S503).
In addition, the channel-coded CB(s) is subjected to rate matching (S504) and the CBs are concatenated (S505).
In a conventional LTE system, a single carrier was configured in uplink or downlink transmission, and a PUCCH of a certain UE was configured and transmitted within the single carrier. Since the uplink transmission is performed by the UE, PAPR should be low in order to reduce battery consumption. Therefore, a modulation scheme with a single carrier feature was used.
However, in an IMT-Advanced system such as an LTE-advanced system, as a UE transmits a larger amount of control information to a base station, large payload symbols need to be simultaneously transmitted via a legacy control channel. Therefore, when the control information transmitted via a control channel or a shared channel in uplink is transmitted in a state of being joint coded, overhead can be reduced and a channel coding gain can be increased. The joint coded control information may be transmitted or received using a multiple-carrier-based transmission scheme or a transmission scheme based on a combination of a single carrier and multiple carriers, in order to perform broadband communication. The UE may be selectively operated in each carrier, or transmit or receive signals simultaneously using several carriers.
Accordingly, when a signal received by a receiver is decoded in the multiple-carrier-based transmission scheme, efforts for reducing power consumption due to the transmission of the multiple carriers without increasing decoding complexity are being made in association with the scheme.